The present invention relates generally to a semiconductor light emitting element, a semiconductor light emitting device including especially a semiconductor light emitting element for emerging deflected light beams exhibiting luminous characteristics blue through infrared-ray areas, and a method of manufacturing the semiconductor light emitting element.
A semiconductor light emitting device having a semiconductor light emitting element such as an LED (Light Emitting Diode), is used for an outdoor display lamp, a signboard, a traffic signal and a display for displaying operations and states of a variety of appliances.
FIG. 19 shows an example of a sectional structure of the prior art semiconductor light emitting element composed of an InGaAlP material group. This semiconductor light emitting element includes an n-GaAs substrate 1 on which a reflection layer 2 consisting of ten pairs of n-GaAs/n-In.sub.0.5 Al.sub.0.5 P, an n-In.sub.0.5 (Ga.sub.0.3 Al.sub.0.7).sub.0.5 P cladding layer 3, an n-In.sub.0.5 Ga.sub.0.5 P active layer 4, a p-In.sub.0.5 (Ga.sub.0.3 Al.sub.0.7).sub.0.5 P cladding layer 5, a p-GaAlAs current diffused layer 6, a p-GaAs contact layer 7 in this sequence. Thereafter, an n-electrode (a substrate side electrode) 8 is provided under the semiconductor substrate, and a p-electrode (light emitting side electrode) 11 is provided on the p-GaAs contact layer 7. Thereafter, the whole is formed into pellets by dicing. In this case, a side surface of the pellet assumes a substantially perpendicular or trapezoidal shape corresponding to a configuration of a dicing blade.
FIG. 20 is a sectional view illustrating a semiconductor light emitting device as a product in which the prior art semiconductor light emitting element is employed. FIG. 21 shows a characteristic of a luminous intensity distribution when this semiconductor light emitting device emits the light.
A bed member 27 of a lead 25 including a bowl-like reflector 19 is die-bonded to the semiconductor substrate of a semiconductor light emitting element (a pellet) 10 by use of a conductive bonding agent 26 such as an Ag paste. Thereafter, the p-electrode 11 and a lead 29 are electrically connected through a bonding wire 28 such as an Au wire. Sealed thereafter in a bullet-like resin molded sealing member 30 composed of an epoxy resin are the bowl-like reflector 19, a part of the lead 15, the conductive bonding agent 26, the semiconductor light emitting element 10, the bed member 27, the bonding wire 28, and a part of the lead 29. This resin molded sealing member 30 has functions as a lens and as a member to protect the semiconductor light emitting element 10.
FIG. 21 shows a characteristic of the luminous intensity distribution of the semiconductor light emitting device molded with the bullet-like resin molded sealing member, wherein the axis of ordinate indicates a light intensity (an arbitrary value), and the axis of abscissa indicates a distribution angle of luminous intensity. Light beams from the semiconductor light emitting device are distributed substantially in symmetry in all directions from the center of the bullet-like lens.
Further, in a surface mount type LED lamp (hereinafter referred to as an SMD lamp) constructed such that the semiconductor light emitting element is mounted on an insulating substrate and sealed by transparent resin to form a package, the above semiconductor light emitting element can not be disposed at the center of a product (i.e., the center of the insulating substrate) in a presently prevailing size of 2.times.1.25 mm or 1.6.times.0.8 mm or in a smaller size than these sizes in terms of an assembly design.
For example, a central line L passing through the center of the semiconductor light emitting element 10 shown in FIG. 22, is disposed slightly offset from the central line (viz., the center of the product) of the insulating substrate 20 having a thickness of 0.5 mm. This semiconductor, light emitting element 10 is 0.3.times.0.3 mm in a pellet size. First and second electrode conductors 21 and 22 of the semiconductor light emitting element 10 are formed on the insulating substrate 20, and the semiconductor light emitting element 10 is bonded onto the second electrode conductor 22 by an Ag (silver) paste. The electrode 11 of the semiconductor light emitting element 10 is provided substantially at the center of the semiconductor light emitting element 10. Then, the electrode 11 and the first electrode conductor 21 are electrically connected to each other through an Au (gold) bonding wire 23. The semiconductor light emitting element 10, tips of the first and second electrode conductors 21, 22, and the bonding wire 23 are covered for protection with a housing, i.e., a transparent resin molded sealing member 24 composed of the epoxy resin.
Thus, the central line L of the semiconductor light emitting element is not coincident with a central line O of the insulating substrate. Hence in the prior art SMD lamp, the characteristic of the luminous intensity distribution based on the housing exhibits an asymmetrical characteristic with respect to the center of this product, a peak position of luminance deviates from the center of the product, and the luminance at the center of the product decreases (see FIG. 7A). In FIGS. 7A and 7B, the axis of abscissas indicates a position of the insulating substrate 20 (the center is a substrate center 0), and the axis of ordinates indicates a light intensity (an arbitrary value).
Further, the pellet size of the semiconductor light emitting element has hitherto been normally 300 .mu.m.times.300 .mu.m. This size leads to a reduced possibility of the pellet being cracked and cleaved due to an impact load when mounted and wire-bonded. However, if the pellet size is under 250 .mu.m.times.250 .mu.m, the pellet might easily be subjected to a mechanical damage when mounted, and especially a scribed pellet is conspicuous in terms of this damage.
A method of cutting a compound semiconductor wafer in the pellet-like shape has hitherto involved the use of a dicer for linearly cutting it while rotating a high speed cutter blade formed by embedding diamond particles into a resinous or metal disk. Over recent years, however, there has been used a scribing method defined as a method of cutting the compound semiconductor wafer, which is advantageous in terms of a unit price of the element and processwise as well. The scribing method is, however, a method of dividing into a pellet by applying an external force upon a scribing line, and therefore, the wafer must be small in thickness in order to obtain a good separation rate and a good pellet configuration. Further, what is indispensable for the scribing process might be sufficient examinations about, e.g., a cutting depth thereof and a selection of the surface on which to scribe.
The semiconductor light emitting device using the conventional semiconductor light emitting element described above, has the characteristic in which the luminous intensity distribution is asymmetric. Therefore, for instance, the light emitting device is attached to a road information plate provided just above the road, it is required that the light emitting device be attached with a slight inclination downward so that the center of the luminous intensity distribution is directed to a vehicle passing through. Further, another method requires a molding process of making a lens design such that the luminous intensity distribution is deflected as an asymmetric characteristic.
Moreover, the prior art semiconductor light emitting element is structured so that the pellet is obtained by dicing the wafer, the side surface of this pellet is etched enough to form a rough state of this surface. It is known that a light emitting efficiency is enhanced with such a structure. The etching process on the side surface, however, decreases a light emitting area (a pn-junction area) of the pellet, and the number of manufacturing steps increases, which problem might cause many disadvantages.
Furthermore, according to the scribing method in the prior art, the surface of a semiconductor crystal layer stacked on the substrate is scribed. In this case, if split into the element by applying the external force after being scribed, a separation rate thereof is as remarkably bad as approximately 70%. For the purpose of improving this rate, there is contrived, e.g., a scribing method of scribing it by increasing a pressure applied upon a scribing diamond needle to give a sufficient cut depth by scribing. When increasing the pressure exerted on the scribing diamond needles, a scribed damage spreads over the crystal surface, resulting in a damage that is twice through four times as large as the scribing line width. This damage might cause the crack and chipping of the edge of the pellet when divided into the element by applying the external force, which tends to lower reliability. Another problem is that the pellet is unable to take a neat configuration.
What is thinkable otherwise is a method of scribing the substrate crystal. A point to which the attention is paid about this method is a prediction that the scribing line on the side of the substrate as a starting point of separation when divided into the element by applying the external force, is more advantageous for the reason that the crystal layer stacked by an epitaxial growth, it can be considered, exhibits a high viscosity due to a good crystallinity with respect to the substrate crystal. There exists, however, only a typical scribing device as the one capable of monitoring just only the surface on which to scribe, and it is highly difficult to coincide the scribing line on the side of the substrate crystal with an element pattern on the side of the stacked semiconductor crystal layer.
Further, the compound semiconductor wafer that has hitherto generally been used is 200 .mu.m-300 .mu.m. Then, a planar configuration of the pellet separated from the wafer is substantially square, and a crosswise dimension (a length-of one side of the square) is also 200 .mu.m-300 .mu.m. Namely, a general shape of the conventional pellet is substantially a cube. When obtaining such a pellet by dividing the wafer, in the step of being into the pellet by applying the external force after executing the scribing process, the separation rate is quite low because of the thickness being substantially uniform and comparatively large for the crosswise dimension of the pellet, and, even if separated therefrom, an occurrence rate of the defect such as the chipping in the pellet enough to be unusable is not small.